This application is based upon and claims the benefit of priority from the prior Japanese Patent Applications JP2001-284841 and JP2001-284842 both filed on Sep. 19, 2001, the entire contents of which are incorporated herein by reference.
The inventions described herein relate to a high pressure discharge lamp which is provided with a light-transmissive discharge vessel made of ceramics (hereinafter, referred to as light-transmissive ceramic discharge vessel) and a luminaire using such a high pressure discharge lamp.
In recent years, a metal halide lamp equipped with a light-transmissive ceramic discharge vessel has been in widespread use. Such a metal halide lamp has features that the color temperature change and the dispersion of colors in lifetime are scarce in compared with a metal halide lamp equipped with a conventional silica glass discharge vessel, in addition to the features of having a longer life-expectancy and a high lighting efficiency
Conventional light-transmissive ceramic discharge vessels used for high pressure discharge lamps (prior-art I), such as metal halide lamps equipped with a light-transmissive ceramic discharge vessel, often have a structure wherein a cylindrical portion, a large-diameter cylindrical portion, and a tubular portion are assembled by shrink-fitting. In this configuration, a tubular portion forms slender cylindrical portion for the swollen portion in which, as for a light-transmissive ceramic discharge vessel, a cylindrical portion and a large-diameter cylindrical portion surround discharge space, respectively. The high pressure discharge lamp equipped with the configuration of light-transmissive ceramic discharge vessel has little change of the color-temperature when changing the lighting position. This is because the change of the coldest portion temperature is small. In the conventional high pressure discharge lamp as mentioned above, the coldest portion is defined in the vicinity of the end of a tubular portion. The temperature of this portion is determined by the balance of the conductive heat and the radiant heat from the electrodes, and the conductive heat from the light-transmissive ceramic discharge vessel. Although the conductive heat and the radiant heat from the electrodes hardly change when the lighting position is changed, the amount of heat conduction from the light-transmissive ceramic discharge vessel changes extensively. That is, at a horizontal position lighting, an arc bends upwards and approaches the wall of upper portion of the light-transmissive ceramic discharge vessel. Thus the upper portion is strongly heated. Meanwhile, the heat conductivity of ceramics, such as a light transmissive alumina used for the light-transmissive ceramic discharge vessel, is significantly high as compared with that of silica glasses
Therefore, it is normal to expect that an amount of heat conducted to the end of the slender cylindrical portion where occurs the coldest portion increases, the temperature of the coldest portion rises and thus the color temperature changes. However, the shrinkage fitting portion of the light-transmissive ceramic discharge vessel works as a heat resistance thus limiting in some degree the amount of heat transferred to the slender cylindrical portion where occurs the coldest portion, suppressing the change of the color temperature at a practically allowable level. This is the reason why the change of the color temperature is small when changing the lighting position, that is, the lighting position property is favorable.
On the other hand, in reference document II as disclosed in the Japanese Patents JP9-147803 and JP 11 204086, a light-transmissive ceramic discharge vessel is constructed in one piece by a cast-molding. This type of discharge vessel has a tendency that the heat capacitance goes relatively low. The reference document II is advantageous for keeping favorable the temperature of the coldest portion due to its nature having the relatively low heat capacitance. However, the reference document II still has a problem due to that the heat conductivity of the light-transmissive ceramic discharge vessel is significantly high.
Moreover, the reference document II falls into two categories, i.e., one that the inner surface and the outer surface of the discharge vessel are defined in gently continuous curves at the boundary portion between the swollen portion and the slender cylindrical portion, and another that the inner surface and the outer surface of the discharge vessel are defined in discontinuous inflected surfaces at the boundary portion between the swollen portion and the slender cylindrical portion.
Meanwhile, when lighting the high pressure discharge lamp with a high frequency current, it is necessary to avoid an acoustic resonance and. To that end, it is desirable to unify acoustic resonance modes of the light-transmissive ceramic discharge vessel. In order to realize the unification of the acoustic resonance modes, it is necessary to shape the inner wall of the swollen portion of a light-transmissive ceramic discharge vessel in spherical. However, in the reference document II, particularly the one having a uniform thickness at the swollen portion of the light-transmissive ceramic discharge vessel and a nearly spherical shape, as shown in the Japanese laid-open patent JP9-147803, a discontinuous inflection is defined in both of the inner and the outer surfaces around the boundary portion between the swollen portion and the slender cylindrical portion. Furthermore, since the electrode reaching a high temperature during lamp operation is located near the inflecting portion, a serious thermal stress occurs in the inflecting portion. Thus, there were problems that the slender cylindrical portion is broken during manufacturing, or a crack easily occurs during lamp operation. As a result of studying measures for solving the problems, the present inventors have found that when the inner surface and the outer surface of the discharge vessel are defined in gently continuous curves at the boundary portion between the swollen portion and the slender cylindrical portion, the mechanical strength of the boundary portion is improved and thus the problems can be eliminated.
In the shrink-fit structure shown in reference document I there is a tendency that a heat capacitance relatively increases. Therefore, when lamp wattage being reduced, there is a problem that it is impossible to maintain the coldest portion in a temperature required for securing high efficiency.
Further, the structure in that the inner surface and the outer surface of the discharge vessel are defined in gently continuous curves at the boundary portion between the swollen portion and the slender cylindrical portion in the prior-art II also fail to solve the problem regarding the lighting position property. That is, since when the inner and the outer surfaces around the boundary portion between the swollen portion and the slender cylindrical portion are both continuous surfaces the conductive heat and the convective heat during lamp operation become easy to be transferred to the coldest portion through the boundary, the problem of the lighting position property becomes serious. When increasing the amount of a metallic halide in the discharge vessel to reduce the problem of the lighting position property, it is effective since the metallic halide becomes hard to move when changing the lighting position. However, this causes an opposite difficulty that impurities, such as H2O, becomes easy to mix into the metallic halide, thus remarkably deteriorating the lamp property during life.
Our inventors have found that when a starting-aid conductor, i.e., a metal coil having the same potential as the opposite side the electrode is wound on a slender cylindrical portion, a weak discharge occurs across the coil and the electrode penetrating the slender cylindrical portion at the start of operation and thus the starting operation is aided.
In this configuration, a capacitive coupling is formed between the starting-aid conductor and the electrode surrounded by the starting-aid conductor. Then, a precursive week discharge occurs through the capacitive coupling, and promotes the starting operation. The capacitance of the electrostatic coupling is effective to achieve a proper glow-arc transition time (0.5-3 seconds). However, the above configuration has a problem that when a week discharge has occurred, a thermal shock is given to the boundary portion between the swollen portion and the slender cylindrical portion. Thus, there is a problem that a crack is easy to occur on the boundary portion.
Furthermore, by providing starting-aid conductors on the pair of slender cylindrical portions of the light-transmissive ceramic discharge vessel, respectively, it is expected that the property will be further improved. However, actual glow-arc transition times at the pair of the electrodes are different each other if the coil turns of the starting-aid conductors are equalized each other. Accordingly, the electrode in the side related to the shorter glow-arc transition time is fed a power required for the glow-arc transition in a short time. Accordingly, the electrode is overheated and then the evaporation or the electrode material increases. As a result, there arises a problem that a blackening occurs on the light-transmissive ceramic discharge vessel.
Our inventions provide a high pressure discharge lamp provided with a light-transmissive ceramic discharge vessel which maintains the coldest portion temperature to an optimal value, and suppresses a color-temperature change accompanying the change of lighting position, and a luminaire using such a high pressure discharge lamp.
Our inventions also provide a high pressure discharge lamp which makes easy to avoid acoustic resonance by simplifying the acoustic resonance modes of the light-transmissive ceramic discharge vessel, and hard to cause cracks by thermal stresses on the boundary portion between the swollen portion and the slender cylindrical portion of the light-transmissive ceramic discharge vessel, and a luminaire using such a high pressure discharge lamp.
Our inventions also provide a high pressure discharge lamp which makes hard to cause cracks by thermal stresses according to a precursive week discharge occurred by a starting-aid coil wound on the slender cylindrical portion, and a luminaire using such a high pressure discharge lamp.
Our inventions also provide a high pressure discharge lamp which suppresses a blackening easily occurring on the light-transmissive ceramic discharge vessel by a starting-aid coil wound on the slender cylindrical portion, and a luminaire using such a high pressure discharge lamp.
In one respect the high pressure discharge lamp comprises a light-transmissive ceramic discharge vessel having a swollen portion defining a discharge space and a pair of slender cylindrical portions formed in integral with the swollen portion and communicating with the swollen portion at opposite ends of the swollen portion, wherein the inner surface of the boundary portion between the swollen portion and the each slender cylindrical portion defines a continuous curved surface, a pair of electrodes, wherein one of the pair electrodes penetrating the respective one of the pair slender cylindrical portion of the light-transmissive ceramic discharge vessel and lie in the swollen portion of the light-transmissive ceramic discharge vessel at their distal ends, lead-conductors connected to the proximal ends of the electrodes, sealed in the light-transmissive ceramic discharge vessel at least at their mid-portions and exposing outside from the light-transmissive ceramic discharge vessel at their proximal ends, and a filling filled in the light-transmissive ceramic discharge vessel.
Still another aspect of the high pressure discharge lamp according to our inventions is further characterized by that the minimum wall-thickness Tmin of the light-transmissive ceramic discharge vessel is equal to or more than 0.1 mm, and the inner diameter D of the swollen portion and the curvature radius R of the concave outer surface around the boundary portion between the swollen portion and the slender cylindrical portion satisfies an equation 0.1xe2x89xa6R/Dxe2x89xa61.5.
Still another aspect of the high pressure discharge lamp according to our inventions is that the minimum wall-thickness Tmin of the light-transmissive ceramic discharge vessel is equal to or more than 0.3 mm, and the inner diameter D of the swollen portion and the curvature radius R of the concave outer surface around the boundary portion between the swollen portion and the slender cylindrical portion satisfies an equation 0.1xe2x89xa6R/Dxe2x89xa61.5.
Still another aspect of the high pressure discharge lamp according to our inventions is that the inner diameter D of the swollen portion and the curvature radius R of the concave outer surface around the boundary portion between the swollen portion and the slender cylindrical portion satisfies a following equation 0.1xe2x89xa6R/Dxe2x89xa61.5, the rated lamp wattage is equal to or less than 50W, and the rated lighting frequency is in the range of 15 to 30 kHz or the range of 40 to 50 kHz.
We also provide a luminaire including a luminaire main-body, a high pressure discharge lamp with a rated lamp wattage equal to or less than 50 W and a configuration as defined in any one of the above aspects of the high pressure discharge lamps, which is mounted on the luminaire main-body, and a lighting circuit for driving the high pressure discharge lamp, at a rated lighting frequency in the range of 15 to 30 kHz or the range of 40 to 50 kHz.
In this application, some definitions and their technical meanings are presented for following specific terms, unless otherwise specified.
The term xe2x80x9clight-transmissive ceramic discharge vesselxe2x80x9d means a hermetic discharge lamp swollen portion comprised of a mono-crystalline metal oxide, e.g., a sapphire, a polycrystalline metal oxide, e.g., a semi-transparent aluminum oxide, and yttrium-aluminum garnet (YAG), an yttrium oxide (YOX) and a polycrystalline non-oxidic material, e.g., a material having a light-transmissivity and heat-resistancy like aluminum nitride (AIN). Here, the term xe2x80x9clight-transmissivexe2x80x9d means a transmissivity allowing light generated by a discharge to be led outside. Accordingly the term may include not only a transparency but also a light-diffusiveness. In addition, it is essential that at least the swollen portion has a transmissivity. While if required the small-diameter cylinder may have a light blocking effect.
Moreover, the light-transmissive ceramic discharge vessel is provided with a swollen portion defining a discharge space and slender cylindrical portions communicating with the swollen portion at opposite ends of the swollen portion. And the swollen portion and the slender cylindrical portions are united in one piece. Therefore, there is no heterogeneous structure in the glass material section by shrink-fitting. Since the swollen portion defines a discharge space, the inner surface of the swollen portion can be a continuous curved surface. Furthermore, the principal part of the inner surface of the swollen portion can be made into a spherical hollow. It is desirable that the xe2x80x9cspherexe2x80x9d is a perfect sphere since in such a perfect sphere an acoustic-resonance frequency becomes a single mode. However, the inner surface can be an oval sphere if required. In addition, the xe2x80x9cprincipal partxe2x80x9d of the swollen portion denotes a residual major part of the swollen portion except the end portion next to the slender cylindrical portion, where the discharge light principally transmits there-through.
Secondly, the thin cylinder portion contributes to secure a coldest portion therein by leaving a narrow gap so-called a capillary between a later described the electrode penetrating inside the thin cylinder portion, and to seal the swollen portion. The inner diameter of the thin cylinder portion is preferable to be equal to or less than 1 mm for lowering the thermal capacitance as much as possible. It is more preferable that the inner diameter is equal to or less than 0.8 mm. In addition, the section of the slender cylindrical portion is preferable to be approximately round shape.
According to one aspect of the inventions, the boundary portion between the swollen portion and the slender cylindrical portion of the light-transmissive ceramic discharge vessel defines the discontinuous inflection. Then, it becomes possible to constitute the swollen portion in an almost spherical shape. Consequently acoustic-resonance frequency is simplified. In case of lighting a high pressure discharge lamp with a high frequency current, the operation frequency is conventionally set to fall in a frequency band which exists between the secondary and tertiary harmonics of the acoustic-resonance frequency. According to this aspect of the invention, the frequency band spreads in the range of 9 to 10 kHz which is broader by about 2 kHz than that of the conventional case. Thereby, the design of the high frequency lighting circuit becomes easy. Here, the term xe2x80x9calmost spherical shapexe2x80x9d means substantial spherical. That is, some extent of deformation occurring in manufacturing process is permitted.
However, it is more favorable that the inner wall of the swollen portion has a sphericity of 0.53 or more.
Referring now to FIG. 1, the term xe2x80x9csphericityxe2x80x9d will be described.
FIG. 1 is a drawing for explaining the sphericity of the swollen portion of the light-transmissive ceramic discharge vessel in the high pressure discharge lamp according to the present invention. In FIG. 1, the numeral xe2x80x9c1xe2x80x9d denotes a light-transmissive ceramic discharge vessel. The numeral xe2x80x9c1axe2x80x9d denotes a swollen portion. The numeral xe2x80x9c1bxe2x80x9d denotes a thin portion. The letter xe2x80x9cXxe2x80x9d denotes a central axis. And the letter xe2x80x9cYxe2x80x9d denotes an axis orthogonal to the central axis X.
The swollen portion 1a has a maximum inner diameter D along the axis Y, and an axial length La along the central axis X. Further, let the intersection of the axis Y and the inner surface of the swollen portion 1a be xe2x80x9cP1xe2x80x9d, and let the point where the line extending from the intersection P1 towards the central axis X touching internally with the boundary portion between the swollen portion 1a and the slender cylindrical portion 1b be P2. When letting further the right and left two intersections where the line 1 extending between the intersections P1 and P2 intersects the central axis X be P3, the axial length La of the swollen portion 1a is given by the distance between the right and left intersections P3, P3.
Then the sphericity IG of the swollen portion 1a is given by a following equation, from the maximum inner diameter D and the axial length La.
IG=D/La
Meanwhile, the sphericity IG is determined by the mean value of the maximum value and the minimum value among the values obtained for a plural locations around the central axis X.
According to that in this aspect of the invention the sphericity IG of the swollen portion of the light-transmissive ceramic vessel is 0.53 or more, the fundamental acoustic-resonance frequency is simplified. Therefore, when the high pressure discharge lamp according to this aspect of the present invention which is manufactured by using the above configuration of the light-transmissive ceramic discharge vessel, it becomes easy to light the high pressure discharge lamp at a frequency getting out of the acoustic-resonance frequency. That is, it become possible to light the high pressure discharge lamp at a specific high frequency. Meanwhile, a desirable sphericity is in the range of 0.53 to 0.85, and a more preferable sphericity is in the range of 0.57 to 0.82.
Meanwhile, still another aspect of the high pressure discharge lamp is characterized by that the wall-thickness ratio Tmin/Tmax of the minimum wall-thickness Tmin and the maximum wall-thickness Tmax of the light-transmissive ceramic discharge vessel is restricted to 0.75. If the wall-thickness ratio Tmin/Tmax exceeds 0.75, a required degree of heat accumulation effect fails to obtained. By the way, the wall-thickness ratio Tmin/Tmax is favorable to be 0.65 or less. Thereby, the color-temperature change at the time of changing the lighting position decreases further.
Here, it is more preferable that the wall-thickness ratio Tmin/Tmax of the minimum wall-thickness Tmin and maximum wall-thickness Tmax is regulated to 0.1 or more. Since the heat capacitance of the light-transmissive ceramic discharge vessel becomes excessive when the wall-thickness ratio Tmin/Tmax is less than 0.1, the rising time of the luminous flux at the start of operation becomes slower. Hence, the wall-thickness ratio Tmin/Tmax should not be less than 0.1.
The locations of the thinnest wall portion and the thickest wall portion are not especially restricted. However, it is most reasonable for manufacturing that the location of the thinnest wall portion lies around the portion where the swollen portion has the maximum diameter. It is also most reasonable that the location of the thickest wall portion lies around the boundary of the swollen portion and the slender cylindrical portion. Moreover, the locations of the thinnest wall portion and the thickest wall portion are relative with each other. That is, they do not take any particular importance for achieving the objects of the present invention. However, the minimum wall-thickness must take a value which exhibits a mechanical strength capable of standing against the pressure of the filling in the discharge vessel during the operation of the high pressure discharge lamp. By the way, the thinnest wall portion has a relatively high light transmittance. Therefore, according to that the portion around the widest portion of the swollen portion takes the minimum wall-thickness and thus the effective amount of light passing through that portion is relatively large, the widest portion exhibits a high luminous efficiency. Here, the term xe2x80x9ceffective amount of lightxe2x80x9d means the amount of light usable for illumination among the light radiated from a high pressure discharge lamp.
On the other hand, it is effective that the thickest wall portion lies in the swollen portion, not but in the slender cylindrical portion since the cross-sectional area of the wall of the swollen portion is relatively larger than that of the slender cylindrical portion, and thus takes a large thermal capacitance. While, the thickest wall portion takes a relatively low light transmittance. Accordingly, when giving greater importance to the luminous efficacy it is preferable that the thickest wall portion lies on a location where the available amount of light passes there-through as small as possible. For example, the above configuration can be achieved by locating the thickest wall portion around the boundary of the swollen portion and the slender cylindrical portion. In this configuration, an effect that the mechanical strength of the boundary portion between the swollen portion and the slender cylindrical portion increases is also achieved. Furthermore, since the thickest wall portion is thicker than a wall-thickness exhibiting a mechanical strength capable of standing against the pressure of the filling in the discharge vessel, in general the thickest wall portion is able to be provided by incrementally forming itself.
Moreover, the wall-thickness of the thin cylinder portion is allowed to change at the inflection as a border. Since the inflection causes a steep change of wall-thickness in the slender cylindrical portion of the light-transmissive ceramic discharge vessel, and thus a thermal resistance increases. Thereby, the injection suppresses a heat transfer from the swollen portion to the slender cylindrical portion. Therefore, it becomes easy to control the temperature of the coldest portion. Meanwhile, when the inflection is formed around the boundary portion between the swollen portion and the slender cylindrical portion, it will be easy to manufacture the light-transmissive ceramic discharge vessel.
Meanwhile, in this aspect of the high pressure discharge lamp, the overall length and the internal volume of the light-transmissive ceramic discharge vessel are not especially restricted. However, assuming to achieve a compact high pressure discharge lamp with a 10 to 50 W lamp wattage, the overall length L is desirable to be 35 mm or less, more preferably be 10 to 30 mm. Moreover, the internal volume is favorable to be 0.10 cc or less, and more particularly 0.01 to 0.08 cc.
Under the favor of that this aspect of the invention has the above configuration, the high pressure discharge lamp is able to lower an amount of heat given from an arc to the swollen portion at a horizontal position lighting by appropriately expanding the distance between the midsection of the curvature of the arc and the inner surface of the swollen portion facing thereto.
Meanwhile, further to the above feature of the light-transmissive ceramic discharge vessel, this invention is still structurally featured by that the outer surface of the boundary portion between the swollen portion and the slender cylindrical portion defines a continuous concave surface, other than that the inner surface of the boundary portion between the swollen portion and the slender cylindrical portion defines a discontinuous inflection. The curvature of the concave surface is not especially restricted. However, when letting the curvature radius of concave be R and the maximum inner diameter of the swollen portion be D, it is more effective that they satisfy a following equation.
0.1xe2x89xa6R/Dxe2x89xa61.5
If the ratio R/D in less than 0.1, the mechanical strength of the boundary portion becomes week, and thus the slender cylindrical portion not only tends to break during manufacturing, but also tends to suffer with cracks due to heat cycle in lifetime. Moreover, if the ratio R/D exceeds 1.5, medium such as mercury for fixing lamp voltage in the filling becomes hard to be cooled effectively. Thus, problems tend to arise in manufacturing process.
Furthermore, by letting the inner diameter D and the overall length L of the swollen portion of the light-transmissive ceramic discharge vessel satisfy a following equation, an occurrence of leak in the light-transmissive ceramic discharge vessel is suppressed while maintaining required lamp property.
0.1 less than D/L less than 0.3
When the ratio D/L is less than 0.1, the temperature of the coldest portion becomes difficult to be maintained in a necessary value. Then, a lighting efficiency decreases and thus a desired luminescence color is no longer obtained. Moreover, if the ratio D/L exceeds 0.3, a leak tends to occur in a sealing portion of the light-transmissive ceramic discharge vessel.
Moreover, the overall length L of the light-transmissive ceramic discharge vessel is associated with a lamp wattage W. Then letting the ratio W/L satisfy the following equation, a favorable high pressure discharge lamp can be obtained.
0.5 less than L/W less than 1.8
Here, if the ratio L/W is less than 0.5, a leak tends to occur in a sealing portion of the light-transmissive ceramic discharge vessel. On the other hand, if the ratio L/W exceeds 1.8, the temperature of the coldest portion becomes difficult to be maintained in a necessary value.
Furthermore, the overall length and the internal volume of the light-transmissive ceramic discharge vessel are not especially restricted. However, assuming to achieve a compact high pressure discharge lamp with a 10 to 50 W lamp wattage, and more preferably with a 10 to 30 W lamp wattage, the overall length L is desirable to be 35 mm or less, more preferably be 10 to 30 mm. Moreover, the internal volume is favorable to be 0.10 cc or less, and more particularly 0.01 to 0.08 cc.
Furthermore, the light-transmissive ceramic discharge vessel is favorable to be so designed that the highest temperature on the outer surface of the discharge vessel becomes 1,000 to 1,200 degrees C. during lamp operation.
Still in one aspect of the invention, the minimum wall-thickness Tmin of the light-transmissive ceramic discharge vessel is equal to or more than 0.1 mm. Furthermore, the minimum wall-thickness Tmin of the light-transmissive ceramic discharge vessel is favorable to be equal to or more than 0.3 mm.
These aspects of the invention specify a value for the minimum wall-thickness Tmin of the light-transmissive ceramic discharge vessel. The minimum wall-thickness influences the pressure resistance of the light-transmissive ceramic discharge vessel. It is unfavorable that the minimum wall-thickness Tmin is less than 0.1 mm, since the pressure resistance decreases extensively. By the way, it is especially favorable that the minimum wall-thickness Tmin is equal to or more than 0.1 mm from the aspect of the pressure resistance.
Therefore, according to this aspect of the invention, a high pressure discharge lamp provided with a light-transmissive ceramic discharge vessel with a sufficient pressure resistance is obtained.
Still in one aspect of the invention, the outer surface around the boundary portion between the swollen portion and the slender cylindrical portion defines a continuous concave surface.
Under the favor of that this aspect of the invention has the above configuration, the high pressure discharge lamp is able to avoid problems of decreasing mechanical strengths, such as a breakage of the light-transmissive ceramic discharge vessel, especially the slender cylindrical portion.
That is, in a configuration wherein a discontinuous inflection is defined on the outer surface around the boundary portion between the swollen portion and the slender cylindrical portion of the light-transmissive ceramic discharge vessel, and a starting-aid conductor comprised of a metal coil is wound on the slender cylindrical portion in displaced to the side of the swollen portion, cracks will likely develop due to a precursive week discharge occurring between the starting-aid conductor and the electrode inserted in the slender cylindrical portion. This tendency becomes remarkable in the case where the inner surface around the boundary portion is still defined a discontinuous inflection.
In contrast, under the favor of that in this aspect of the invention the outer surface of the boundary portion between the swollen portion and the slender cylindrical portion defines a continuous concave surface, the discharge vessel exhibits a sufficient mechanical strength even in occurrence of the precursive week discharge in the above configuration of the starting-aid conductor, and thus cracks hardly occur. Moreover, breakages hardly occur in a manufacturing process, and also cracks hardly occur in a heat cycle during the life of the discharge lamp. Meanwhile, in this aspect of the invention, the inner surface around the boundary portion between the swollen portion and the slender cylindrical portion of a light-transmissive ceramic discharge vessel may be a continuous convex surface, or may define a discontinuous inflection.
Still in one aspect of the invention, the inner diameter D of the swollen portion and the curvature radius R of the concave outer surface around the boundary portion between the swollen portion and the slender cylindrical portion are so related to each other to satisfy the following equation.
0.1xe2x89xa6R/Dxe2x89xa61.5
This aspect of the invention specifies a suitable configuration for the concave surface defined in the outer surface around the boundary portion between the swollen portion and the slender cylindrical portion. If the ratio R/D is less than 0.1, the mechanical strength of the boundary portion becomes week, and thus the slender cylindrical portion not only tends to break during manufacturing, but also tends to suffer with cracks due to heat cycle in lifetime. Moreover, if the ratio R/D exceeds 1.5, medium such as mercury for fixing lamp voltage in the filling becomes hard to be cooled effectively. Thus, problems tend to arise in manufacturing process.
Electrode has a slender shape and forms a narrow gap between the inner surface of the slender cylindrical portion of the light-transmissive ceramic discharge vessel by being inserted into the slender cylindrical portion, and its distal end faces the interior of the swollen portion of the light-transmissive ceramic discharge vessel.
Meanwhile, the phrase xe2x80x9cface the interior of the swollen portionxe2x80x9d has a concept containing a state of the distal end lying in the swollen portion and a state of the distal end lying in the slender cylindrical portion communicating with the swollen portion. The electrode can be made by any one or an appropriate combination selected from conductive and refractory materials such as tungsten, rhenium, doped tungsten, tungsten-rhenium alloy, molybdenum, cermet etc. Furthermore, preferably, the electrode can be comprised of a slender the electrode rod and an the electrode principal part located on the distal end of the electrode rod. In this configuration, the electrode principal part is located on the distal end of the electrode rod part, and constitute an tip-end of the electrode which operates as a cathode or an anode.
The tip-end of the electrode could be wound thereon a coil made of pure-tungsten or doped-tungsten, or shaped into a head integrated with the shank part, as needed, so as to enlarge its surface area to enhance heat dissipation.
Meanwhile, the tip-end of the electrode faces the interior of the swollen portion. Here, the phrase xe2x80x9cface the interior of the swollen portionxe2x80x9d has a concept containing a state of the distal end lying in the swollen portion and a state of the distal and lying in the slender cylindrical portion communicating with the swollen portion.
It is desirable that the mid-portion of the electrode has a thickness as uniform as possible so as to leave a narrow gap, i.e., form a capillary between the electrode and the inner surface of the small-diameter cylinder of the light-transmissive ceramic discharge vessel. The mid-portion of the electrode could be wound thereon a coil made of pure-tungsten, rhenium, tungsten-rhenium alloy or doped tungsten. Thereby, the electrode is facilitated to be centered to the slender cylindrical portion.
The proximal end of the electrode is fixed not only to a suitable position of the light-transmissive ceramic discharge vessel so as to work for receiving power from outside, but also to the tip-end of the lead-conductor by welding or the like, so that the electrode is electrically and mechanically supported by the lead, conductor. Here, in order to buffer the heat at the sintering the material such as molybdenum could be interposed between the lead-conductor and the base end of the electrode.
According to one aspect of the inventions, a starting-aid conductor is wound on one slender cylindrical portion of the light-transmissive ceramic discharge vessel for surrounding the electrode penetrating the one slender cylindrical portion and electrically connected to have the same potential as the other electrode opposite to the former electrode.
Here, the term xe2x80x9copposite the electrodexe2x80x9d means an the electrode which faces the other the electrode surrounded by the starting-aid conductor through the slender cylindrical portion through a discharge space in the swollen portion. The starting-aid conductor may be provided for both of or any one of the electrodes. For letting the starting-aid conductor have the same potential with the opposite the electrode, it suffices to connect the starting-aid conductor to the opposite the electrode through, for example, an appropriate conductor.
The lead-conductor works for applying a voltage across the electrodes. The top end of the lead-conductor is connected to the proximal end of the electrode, and the base end is exposed to outside the light-transmissive ceramic discharge vessel. The phrase xe2x80x9cthe base end is exposed to outside the light-transmissive ceramic discharge vesselxe2x80x9d means that it may or may not protrudes outside the light-transmissive ceramic discharge vessel, however, it has to face outside within being supplied the current from outside.
A lead-conductor could use a niobium, a tantalum, a titanium, a zirconium, a hafnium and a vanadium which are an electric leading metal having almost same average thermal expansion coefficient as that of the light-transmissive ceramic. In case of using aluminum oxide such as alumina ceramic as the material of the light-transmissive ceramic discharge vessel, since the niobium and the tantalum have almost same average thermal expansion coefficient as that of the aluminum oxide, they are suitable for sealing. In case of using the yttrium oxide and the YAG, there is no significant difference in their thermal expansion coefficients. In case of using the aluminum nitride for the light-transmissive ceramic discharge vessel, it is better to use the zirconium as the lead-conductor. They contribute to absorb impurity gas left inside the light-transmissive ceramic discharge vessel. Further, the lead-conductor is able to be used for supporting the entire of the high pressure discharge lamp by supporting the electrode.
The lead-conductor could be composed of the sealing metal rod, pipe, or coil of a niobium. In this case, since niobium etc. has an intense oxidation, an oxide-resistant conductor is connected to the lead-conductor and the lead-conductor has to be sealed by a sealant so as not to be exposed to the air when the high pressure discharge lamp is turned on in a condition that it is exposed to the air.
The filling may contain rare-gas as starting gas and buffer gas, metallic halide as luminous substance, metallic halide as lamp voltage fixing medium, and mercury as buffer vapor feed-source, by a following combination thereof. The metallic halide as luminous substance is halide of luminous-metal which emits visible light.
As the lamp voltage fixing medium, mercury or halide can be primarily used. Mercury also contributes as a luminous-metal, in a following case 3. For the halide as the lamp voltage fixing medium, metal yielding a relatively high vapor pressure during operation and a relatively little emission of visible light, for example, Al, Fe, Zn, Sb, Mn etc. is suitable. The rare-gas functions as starting gas and buffer gas. For the rare-gas, a xenon, an argon, or a krypton could be used alone or mixed with any other thereof.
By using neon and argon for the rare-gas, a glow discharge power is reduced. Thereby, a glow-arc transition time may moderately extend. In this case, argon is mixed with the neon in the rage of 0.1 to 10% in the percent pressure. Thereby, evaporation of tungsten constituting the electrodes is depressed, and thus the blackening at the start of operation is remarkably reduced. Since the starting voltage lowers in accompanying that, a lighting circuitry becomes compact in size, light in weight, and less-expensive. Moreover, the rare-gas is filled in the light-transmissive ceramic discharge vessel to exhibit a pressure more than one atmospheric pressure during the operation of the lamp. Here, in this specification the term xe2x80x9chigh pressure dischargexe2x80x9d means a discharge wherein the pressure of the filling during the operation of the lamp becomes higher than the atmospheric pressure that is, it is a concept including a very high pressure discharge.
Further, as buffer vapor, metallic halide which yields a relatively high vapor pressure and radiating a little or little amount of visible lights, for example, aluminum halide may be filled in the discharge vessel, in place of mercury.
1. luminous-metallic halide+mercury+rare-gas: This exhibits a configuration of so-called metal halide lamp.
2. luminous-metallic halide+metallic halide as lamp voltage fixing medium+rare-gas: This exhibits a configuration of so-called mercury-free metal halide lamp avoiding use of mercury which has high environmental load.
3. mercury+rare-gas: This exhibits a configuration of so-called high pressure mercury lamp.
4. rare-gas only (in case of using Xe as the rare-gas): This exhibits a configuration of so-called xenon lamp.
As halogen for the halide of luminous-metal, it is able to use any one of iodine, bromine, chlorine and a fluorine, or any number of them in combination. The halide of luminous-metal is able to be selected from a group of known metallic halide, in order to achieve a radiation provided with a desired lighting characteristics about a luminous color, an average color rendering evaluation index Ra and a luminous efficiency, and further in response to the size and the input power of the discharge lamp light-transmissive ceramic discharge vessel For instance, one or some of halides selected among a group of Na-halide, Li-halide, Sc-halide, Tl-halide and rare-earth metallic halide could be used.
In this invention, although it is not a requirement, a part or all of the following configurations are able to be provided as needed.
Sealing compound for ceramics can be used for closing the light-transmissive ceramic discharge vessel by sealing a gap between the slender cylindrical portion of the light-transmissive ceramic discharge vessel and the lead-conductor penetrating there-through and provided with the electrode on its distal end. For closing the discharge vessel, the sealing compound for ceramics is charged in the gap between the lead-conductor and the slender cylindrical portion from the end of the slender cylindrical portion. The sealing compound for ceramics is then melted by heating and spreads in the gap between the lead-conductor. After that the sealing compound for ceramics is solidified by cooling and consequently hermetically seals the gap between the lead-conductor and the thin cylinder portion. According to the seal, the lead-conductor is fixed to a predetermined position.
The lead-conductor is desired to be completely covered its portion lying in the thin cylinder portion with the seal. Further, when covering with the seal the proximal end of the slender the electrode fixed to the lead-conductor for a small distance, more preferably for an extent of 0.2 to 0.3 mm, the lead-conductor becomes hard to be eroded by the filling such as halogen.
When the inner diameter of the swollen portion of the light-transmissive ceramic discharge vessel is enlarged relatively, and the distance between the electrodes is also relatively enlarged corresponding to enlargement of the inner diameter of the enclosure, the starting voltage of the high pressure discharge lamp tends to rise. Thus, by placing a starting-aid conductor, as needed, it is able to reduce the starting voltage. The starting-aid conductor may be a metal coil which is wound around at least one of the slender cylindrical portions through which one the electrode extends, and connected to the other the electrode to have the same potential with the other the electrode which faces the one the electrode through a discharge space in the swollen portion.
The high pressure discharge lamp according to the prevent invention is able to be constituted to be lighted in a state that the light-transmissive ceramic discharge vessel is exposed into air. However, if needed, it is able to accommodate the light-transmissive ceramic discharge vessel in the jacket bulb hermetically. In addition, by using the inner surface of the jacket bulb as a reflecting surface which takes its focus on the light-emitting portion of the high pressure discharge lamp, it is able to achieve a directional lighting high pressure discharge lamp.
The high pressure discharge lamp according to the present intention is easy to collect light and advantageous in an optical configuration, since it could reduce the size of the light source as compared with an incandescent-lamp shaped fluorescent-lamp. The light source could also be integrated with a reflector, as desired. In this case, the reflector may be formed on the inner surface of the jacket bulb which accommodates the light-transmissive ceramic discharge vessel therein. Otherwise, the high pressure discharge lamp may be attached in the reflector which is formed separately. Moreover, the reflector can be provided without using the jacket-bulb.
When letting the diameters of the lead-conductor and the electrode be xcfx86s mm and xcfx86e mm, a following equation may be satisfied.
0.2xe2x89xa6xcfx86e/xcfx86sxe2x89xa60.6
In order to prevent the corrosion of the sealant by the halides by decreasing the temperature of the sealant of the sealing compound for ceramics, and improve the lighting efficiency by increasing the temperature of the narrow gap, the heat resistance is decreased by thicken the lead-conductor in one hand, and the heat resistance of the electrode is increased in other hand. Here, if the thickness ratio xcfx86e/xcfx86s is lower than 0.2, the electrode is too much thin. On the other hand, if the ratio xcfx86e/xcfx86s is higher than 0.6, the temperature of the sealant and the narrow gap can not be maintained at a specific value
If letting the interior volume of the light-transmissive ceramic discharge vessel be 0.1 cc or less, and more preferably be 0.07 cc or less, and letting the average linear transmittance of the light-transmissive ceramic discharge vessel be 10% or more, and more particularly be 30% or more. Here, it is assumed that the linear transmittance is measured in a wavelength of 550 nm. Further, the term xe2x80x9caverage linear transmittancexe2x80x9d means an average value of the linear transmittance data measured at different five sampling points. Furthermore, the interior volume of the light-transmissive ceramic discharge vessel is measured in a following way. First, the swollen portion is submerged in water to fill the water in the enclosure. Then the swollen portion is drawn out from water after the openings of both the thin cylinder portions having been closed. Then the volume of the water in the swollen portion is metered and measure.
In case of the light-transmissive ceramic discharge vessel having small interior volume as mentioned above, if the average linear transmittance of its envelope is 10% or more, it is able to enhance not only the optical efficiency (overall apparatus optical efficiency) including that of an optical system such as a reflector to be combined with the discharge lamp, but also to reduce occurrences of the cracks in the light-transmissive ceramic discharge vessel.
The present invention is effective for a compact metal halide lamp with a rated lamp wattage of less than 50 W, for example, around 10 to 50 W. However, it is more effective for such lamp with 10 to 30 W of lamp wattage. Moreover, the bulb-wall load is preferable to be in the range of 15-50 W/cm2.
It is effective that the narrow gap is equal to or more than 0.21 mm or more.
In order to obtain a high pressure discharge lamp of the lamp wattage lower than 50 w, compact, longer lasting and having a high lamp efficiency, it is found that it is unable to obtain a favorable discharge lamp even if the size of the conventional discharge lamp had been proportionally reduced.
So, by setting the narrow gap as mentioned above, the heat resistance of the electrode is increased, and the amount of heat transferred from the discharge plasma or the electrode is decreased, so as to decrease the temperature of the sealant. Therefore, the lamps hardly cause a leak at their sealants.
When this aspect of the invention has the above configuration, a discontinuous inflection is defined on the inner surface around the boundary portion between the swollen portion and the slender cylindrical portion of the light-transmissive ceramic discharge vessel, the boundary section thus thickened has a large thermal capacitance. As a result, the discharge space and the coldest portion are thermally isolated. Accordingly, since the transfer or halide decreases, the temperature of the coldest portion defined in the slender cylindrical portion is stabilized. Thereby, the lighting position characteristic of a high pressure discharge lamp is improved. Consequently, the maximum color-temperature change accompanying the change of lighting position can also be made within the range of xc2x1150 degree K.
The starting-aid conductor may be comprised of a first and second metal coils which are configured as follows. That is, the first metal coil is wound around one slender cylindrical portion through which the first the electrode penetrates, and connected at its one end to the second the electrode so as to have the same potential therewith. The second metal coil is wound around the other slender cylindrical portion through which the second the electrode penetrates, and connected at its one end to the first the electrode so as to have the same potential therewith.
It is effective that the starting-aid conductors are each so provided that its one end lies in the vicinity of the boundary portion between the swollen portion and the slender cylindrical portion of the light-transmissive ceramic discharge vessel. The starting-aid conductor may be comprised of a metal coil, conductive cover layer, and etc.
Now, A preferred configuration of the starting-aid conductor which is comprised of a metal coil will be described. In implementation thereof, one or some of the following configurations are properly may be adopted.
1. Let the number of turns in the metal coil be four turns or more.
2. Let the winding pitch of the metal coil be 100 to 500%.
3. When letting the lengths of the metal coil and the slender cylindrical portion be LSA1 and LSA2, let the ratio LSA1/LSA2 be 0.3 to 1.0 (see FIG. 8).
Furthermore, since in the light-transmissive ceramic discharge vessel the inner surface around the boundary portion between the swollen portion and the slender cylindrical portion thereof defines a discontinuous inflection, and while the outer surface around there defines a continuous concave, the mechanical strength of the boundary portion is improved as described before. Thus, problems of cracks occurring around the boundary portion of the swollen portion and the slender cylindrical portion due to thermal stresses according to the precursive week discharge between the starting-aid conductor provided on the slender cylindrical portion and the electrode are reduced. Here it is to be understood that the discharge starting property of the high pressure discharge lamp is improved by providing the starting-aid conductor.
A pair of starting-aid conductors comprised of metal coils which are wound on the slender cylindrical portions of the light-transmissive ceramic discharge vessel for surrounding the electrodes penetrating the slender cylindrical portions and are asymmetrical with each other.
Here, the phrase xe2x80x9ca pair of starting-aid conductors are asymmetrical with each otherxe2x80x9d means that they are asymmetrically constructed so as not to have the same starting-aid property. One configuration for the starting-aid properties being different from each other is realized by differing the capacitances between the starting-aid conductors and the electrodes covered by the starting-aid conductors via the slender cylindrical portions. The capacitance is varied by varying any one or more of the distance between the starting-aid conductor and the electrode, the relative dielectric constant of the slender cylindrical portion, and the effective opposing area of the starting-aid conductor and the electrode. The effective opposing area of the starting-aid conductor and the electrode can be easily chanced the effective area of the starting-aid conductor. For example, when the starting-aid conductor is comprised of a metal coil, the capacitance can be varied by changing the number of turns of the metal coil, the wire diameter of the coil wire, or the winding pitch of the metal coil.
Meanwhile, a suitable glow-arc transition time of the arc arising across the pair of the electrodes at the start of operation is about 0.5 to 3 seconds. However if the transition time is shorter than the suitable time, an electric power required for causing the glow-arc transition is supplied in a short time. Then the electrodes are over-heated, and thus an excess amount of the electrode evaporation is caused and thus accelerates the blackening. Such a phenomenon occurs by that an amount of the filling in the high temperature side slender cylindrical portion, and the grow discharge power supplied to the electrode penetrating through the high temperature side slender cylindrical portion fails to be consumed as an energy for evaporating the filling at a time of occurring a precursive week discharge.
In contrast, according to this aspect of the invention, the starting-aid conductor provided in the slender cylindrical portion, like the top side slender cylindrical portion wherein the temperature thereof rises during the operation of the lamp can be structured in asymmetrical to the opposite side starting-aid conductor so as that the capacitance associated to the top side starting-aid conductor increases.
Then, the capacitance between the asymmetrically-structured starting-aid conductor and the electrode surrounded by increases. Accordingly, the precursive week discharge current at the start of operation that starting-aid conductor by this becomes large, it follows on this and the outrider fine discharge current at the start of operation relatively increases. As a result, the energy consumed for evaporating the filling increases. Thereby, heating of the electrode is suppressed, and the blackening is also suppressed.
When this aspect of the invention has the above configuration, the maximum thickness portion serves as a heat accumulating part. According to the heat accumulation effect in that section, the change of the coldest portion temperature, i.e., the change of the color-temperature when changing the lighting position is suppressed.
Moreover, when the inner surface of the swollen portion adopts the composition which forms the continuous curved surface, distance of the central part of the bend of an arc and the inner wall of the swollen portion which counters this can be enlarged at a horizontal position lighting, and the amount of heat transferred from an arc can be reduced.
Still one aspect of the invention specifies a suitable configuration of the high pressure discharge lamp which has a relatively low lamp wattage, and thus capable of lighting at a high frequency. That is, when the rated lamp wattage 50 W or less, it is favorable that the inner diameter of the swollen portion of the light-transmissive ceramic discharge vessel is set in the range of 2 to 6 mm.
Now the reason for specifying the above range for the rated lighting frequency in one aspect of the high pressure discharge lamp will be described below. When it is a frequency lower than 15 kHz, there arises a fear of causing an audible frequency noise. When it is a frequency around 30 kHz, the frequency falls in the range which is popularly used for infra-red remote controllers. Therefore, such a frequency should not be adopted for avoiding malfunctions of infra-red remote controllers. When it is a frequency in the range in excess of 30 kHz and below 40 kHz, the frequency also falls in the range containing an acoustic-resonance mode of the light-transmissive ceramic discharge vessel. Therefore, such a frequency should not be adopted for avoiding acoustic-resonance. When it is a frequency of 50 kHz or over, an interval of the frequency which generated an acoustic-resonance becomes narrower. Therefore, it becomes difficult to adjust the frequency while considering a dispersion of the frequency of lighting circuits.
Then, this aspect of the invention can provide a low lamp wattage high pressure discharge lamp which lights at a high frequency without a practical problem, such as audible noises, acoustic-resonance, and malfunctions of infra-red remote controllers.
We also provide a luminaire useful for the high pressure discharge lamp as described above.
Here, in this application, the term xe2x80x9cluminairexe2x80x9d has a wide concept containing all of such devices using lights radiated by high pressure discharge lamps for any purpose. For example, the luminaire according to this aspect of invention is able to be applied for incandescent-lamp shaped high pressure discharge lamps, lighting equipments, mobile-use head-lights, optical fiber-use light sources, image projectors, photo-chemical devicce, fingerprint discriminators, etc. Here, the term xe2x80x9cluminaire main-bodyxe2x80x9d means reminders of the luminaire from that the high pressure discharge lamp is removed.
The term xe2x80x9cincandescent-lamp shaped high pressure discharge lampxe2x80x9d means a luminaire in which a high pressure discharge lamp and a stabilizer thereof are integrated together, and a bulb-base is added thereto for receiving a commercial power. By loading the bulb-base to a corresponding lamp socket, this type of lamp device is used as if it is a incandescent lamp. In case of constructing the incandescent-lamp shaped high pressure discharge lamp, it is able to provide a reflector for obtaining a required light distribution from the high pressure discharge lamp. Furthermore, it is able to provide a light diffusion glove, or a cover for moderately reducing the brightness of the high pressure discharge lamp. Furthermore, it is able to use a bulb-base having a desirable requirement. Accordingly, for replacing directly with conventional light lamps, a bulb-base the same as that of the conventional light lamps is able to be adopted.
The lighting circuit may be any configuration of an AC lighting and a DC lighting. Moreover, the AC lighting may be any configuration of a high frequency lighting and a low frequency lighting. However, as the swollen portion and the slender cylindrical portion are united in a single body of the light-transmissive ceramic discharge vessel, and the light-transmissive ceramic discharge vessel is suitable for the high sphericity configuration of the swollen portion, it is easy to avoid an influence of the acoustic resonance, the high pressure discharge lamp according to the present invention is preferable for the high frequency lighting in the range of around 5 to 200 kHz.
In the case of high frequency lighting, an inverter can be used for a high frequency generator. As the inverter, it is able to be use a various types of inverter, such as a half-bridge type inverter or a full-bridge type inverter. Although, as a current limiting impedance element, it is able to use any one of an inductance element, a capacitance element and a resistance element, or any number of them in combination, an inductance element is most preferable for a practical application. As an inductance element, it is able to use an inductor, a leakage transformer, etc. Here, in the case of the high-frequency lighting, a circuit configuration wherein a load circuit of the lighting circuit is provided with a resonance circuit which is comprised of the current limiting inductance and a capacitor, and thus the lighting circuit exhibits a load characteristics continuous from a secondary open-circuit voltage to a secondary short-circuit current is especially preferable for the lighting circuit, since it is able to make the lighting circuit compact in size and light in weight.
In contrast, in a low-frequency lighting, it is preferable that the lighting circuit is principally comprised of a step-up or step-down chopper, and a full-bridge type inverter which is energized by the DC output voltage of the chopper. In the above configuration of the lighting circuit, an inductance of the chopper works as a current limiting inductance. Therefore, the lighting circuit does not need a concrete configuration of the current limiting inductance.
Moreover, in the case of the DC lighting, a circuit configuration wherein a high pressure discharge lamp is coupled across the output terminals of the step-up or step-down chopper is preferable for the lighting circuit, since it is able to make the lighting circuit compact in size and light in weight.
Meanwhile, the lighting circuit may be mounted in the luminaire body, or on a suitable location separated from the luminaire body, for example, in the ceiling.
Further details and specific embodiments of the inventions will be apparent to persons skilled in the art from a study of the following description and the accompanying drawings, which are hereby incorporated in and constitute a part of this specification.